Red cell sodium countertransport and cotransport in normotensive and hypertensive blacks

Abstract

We have previously described elevated Lii-Naocountertransport (CT) and Na-K cotransport (CO) in red cells of Caucasian patients from Boston. In this study, we report both transport systems in black patients from Philadelphia. The maximal rate (Vmax) of CT was assayed by measuring the Nao-stimulated Li efflux from cells containing ±6 mmol Li/liter. The Vmaxof outward cotransport was assayed by measuring the furosemide-sensitive component of Na and K efflux into Mg medium from cells containing 50 mmol/Iiter of both ions. The mean value of CT for 18 normotensive (NT) subjects with no family history of hypertension, (-) FHH, was 0.18 ± 0.05 (mmol/liter cells × hour); and in 14 hypertensive (HT) patients, 0.18 ± 0.07. The mean values of Na and K cotransport were, respectively (mmol/liter cells x hour), in 18 NT subjects with (-) FHH, 0.38 ± 0.24 and 0.50 ± 0.28 in 18 HT subjects, 0.25 ± 0.17 and 0.24 ± 0.14. We conclude that there is no difference in the Vmaxfor CT between the two groups of black subjects, but that the Vmaxfor Na-K CO was significantly reduced in the HT group. Notably, the offspring of HT patients (age 14 years, n = 17) also had a marked reduction in the Vmaxof Na (0.15 ± 0.17) K cotransport (0.19 ± 14) in comparison with the mean value of Na (0.40 ± 072) and K (0.60 ± 0.3) cotransport measured in offspring (n = 10) of NT subjects (age 14 years). Two main differences between the patterns of red cell cation transport were found in this sample of black patients in comparison with previous studies in Caucasian subjects. First, hypertensive blacks had no significant elevation of Li-Na countertransport, as previously observed in Caucasians; second, the Vmaxof Na-K cotransport was significantly lower in hypertensive blacks than a previous sample of hypertensives. These measurements of red cell cation transport have uncovered heterogeneity in the types of disturbances of Na transport that might be present in the hypertensive population in different frequencies. The results indicate that in this subset of black hypertensive patients and their offspring, the capacity to transport Na against its electrochemical gradient is lower than in hypertensive subjects with elevated countertransport and Na-K cotransport. © 1984 American Heart Association, Inc.